The telephone system in most countries, such as the United States, includes a number of connected networks. For example, local exchange carriers (LECs) may maintain wireline telephone connections for users in one or more local access and transport areas (LATAs), where a LATA is a geographical area defined by regulation. Interexchange carriers (IXCs), frequently called long distance carriers, may provide inter-LATA communication services. Still further, wireless carriers may operate networks that serve mobile users.
Different networks in the telephone system, such as networks of various carriers, are connected to one another so that calls can be completed between calling and called parties regardless of the network from which a call originates or is destined. Carriers may charge fees to one another when completing a call initiated on another carrier's network.